This invention relates to area radio communication which is capable of readily establishing radio channels where no communication networks are available. The radio communication channels are established via a base station having a communication or service area between first and second stations of a plurality of terminal stations present in the communication area. More particularly, this invention relates to an area radio communication method, an area radio communication network, a base station of the area radio communication network, and to each terminal station of the area radio communication network.
The area radio communication is implemented, for example, by a satellite communication network. It is possible by the satellite communication network to cover a wide communication area on the earth's surface by installing terrestrial stations in the communication area. In such a satellite communication network, it is advantageous for raise of an antenna gain and for the possibility of frequency reuse to make a transponder emit spot beams to the terrestrial stations. It is advantageous on the other hand for compactness of each terrestrial station to establish the radio communication channels in accordance with a frequency division multiple access (FDMA) technique.
In the manner which will later be described in greater detail, a satellite station is disclosed for use as a transponder in Japanese Patent Prepublication (A) No. 62,739 of 1985. From the terrestrial stations working as source stations, N uplink radio signals are directed to the satellite station as frequency division multiplex (FDM) radio signals, where N represents a predetermined natural number, such as ten. In order to switch the N uplink radio signals into N downlink radio signals transmitted as the spot beams to the terrestrial stations operable as destination stations, the satellite station comprises a frequency division multiplex switching or exchange arrangement comprising N.sup.2 switching elements.
This satellite station is capable of switching the uplink radio signal from an arbitrary one of the source stations to the downlink radio signal directed to a desired one of the destination stations with advantages of the spot beams kept to raise the antenna gain and to raise a channel capacity by use of the frequency reuse. The satellite station is, however, bulky and complicated because the N.sup.2 switching elements are indispensable, each switching element comprising a variable frequency bandpass filter and a variable frequency converter. Moreover, each variable frequency bandpass filter must deal with a frequency band into which an entire radio frequency range of the satellite communication network is divided on an average by N and which is a considerably wide passband. In order to insure a sufficient attenuation out of the passband, a guard frequency band is necessary in proportion to the passband and reduces an efficiency of frequency utilization to, for example, only 50 percent.
Prior to publication of the above-referenced Japanese patent prepublication, a multichannel access (MCA) system was standardized 1982 in Japan and is described in various publications, for example, in (in translation) "Mobile Communication System Handbook" published 1989 by the Electromagnetic Wave System Development Center of Japan. In the manner which will later be described more in detail, the MCA system comprises a terrestrial center station having a communication or service area, a plurality of terrestrial commanding or directive stations in the communication area with each commanding station assigned with a local service area, and at least one mobile station movable in the local service area. The center station transmits and receives radio signals to and from the commanding stations by a center station antenna having no directivity. The center station deals with communication between each commanding station and the mobile stations and between the mobile stations by using a single control channel to automatically select an idle channel of communication channel.
Being given no directivity, the center station antenna has a poor antenna gain and must be fed with an appreciably high radio frequency power. This imposes a restriction on a breadth of the communication area.